Re: [Xen-devel] [PATCH RFC] x86: Add hack to disable "Fake HT" mode

[Jürgen Groß <jgross@xxxxxxxx>]

On 15.11.19 16:05, George Dunlap wrote:
> FTR, please avoid top-posting. :-)
>
> On 11/15/19 2:31 PM, Steven Haigh wrote:
> > Just regarding the use of a system environment variable to turn this
> > feature / bugfix / hack on and off - this would probably break starting
> > the VM via the xendomains script.
> >
> > If the VM definition is in /etc/xen/auto/, then there would be nothing
> > to set the environment variable before the VM is launched - hence it
> > would not be applied and a guest crash would occur...
> >
> > Depending on the VM's settings, this would either continue to start &
> > crash - or just stop again until it could be started with the ENV variable.
> Right.  So a couple of options:
>
> 1. Users of xendomains could set the environment variable in their
> xendomains script
>
> 2. We could add a xl.cfg option.  Unknown xl.cfg entries are ignored
> (for better or for worse); in the future, when the "fake ht" thing is
> replaced, we can either continue ignoring it, or give a useful error
> message saying how it should be changed.
>
> 2a.  We could have the config option *replace* the environment variable;
> in which case we'd leave libvirt users high and dry
>
> 2b. We could have the config option cause xl to *set* the environment
> variable, which should continue to allow other toolstacks (even those
> not using libxl) to potentially work around the issue.
>
> Right now I'm leaning towards 2b, and having it be in a separate patch.
In which case we should consider having a way to set arbitrary
environment variables from the config file in order to avoid this kind
of discussion in future similar cases.


Juergen


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